In 3D-video, each eye of the viewer receives its own stream of images. Each image pair in the stream represents the same scene from a slightly different perspective, creating a 3D experience in the human brain during reproduction. Typically, a pair of synchronized cameras is used for capturing stereoscopic 3D video content. One camera captures the images for the left eye, while the other camera captures the images for the right eye. In this context, 3D-video content is also referred to as stereoscopic video content. Due to the slightly different viewing direction of the left and a right camera in a stereoscopic camera arrangement there is a displacement between two corresponding points in the left and right image resulting from the different camera positions. This displacement between corresponding points in the captured images is commonly referred to as disparity.
To produce high quality stereoscopic video content, stereo cameras must be tightly synchronized so that each pair of images, i.e. the image or frame taken by the left camera and a corresponding image or frame taken by the right camera of a stereoscopic camera arrangement, are taken at the same moment in time. Otherwise camera motion and moving objects in the captured scene will lead to additional erroneous disparities. Human observers are well known to be very sensitive to even small amounts of erroneous vertical disparities. However, altered or erroneous horizontal disparities can also lead to severe distortions in the 3D reproduction of the video content. Further, an erroneous disparity between a left and a right picture in stereoscopic video content can lead to conflicts between monocular occlusions and stereoscopic placement cues as well as hyper-convergence or -divergence. These issues can easily lead to an unpleasant viewing experience similar to erroneous vertical disparities, especially as motion in films tends to be more pronounced in the horizontal direction.
In order to provide tight camera synchronization, stereo cameras are usually equipped with a “genlock” or “sync” input through which a central timing generator unit can send a common sync-signal to each of the cameras to trigger the two capturing processes in a synchronous manner. Nevertheless, a lot of 3D video content suffers from insufficient synchronization. The reasons are manifold and range from hardware failures and tolerances to operator mistakes and editing errors.
As a consequence, proper synchronization in the final stereoscopic video content is one critical area to take care of when producing high quality 3D content. According to the prior art, quality inspection with respect to synchronization is performed manually in most cases. However, this is a costly and time consuming process because the 3D content has to be inspected by an operator and synchronization mismatch has to be determined manually. Accordingly, there is a need for an automatic or semi-automatic inspection allowing detecting a synchronization mismatch in 3D content.